Food casings of regenerated cellulose are widely used for the production of various stuffed food products. Cellulosic casing for production of large diameter sausages such as bologna and the like generally are reinforced with a fibrous web. The present invention, however, is concerned primarily with thin walled unreinforced cellulosic casing as may be used in the production of small diameter sausages such as frankfurters and the like.
For convenience of handling, food casings which may be 20 to 50 meters or more in length are shirred and preferably compressed to produce what commonly are referred to as "shirred casing sticks". Such casing sticks are hollow cylinders about 20 to 60 centimeters in length. Shirring machines for producing these shirred sticks are well known in the art and are disclosed in U.S. Pat. Nos. 2,983,949 and 2,984,574 among others. Shirring and related technology also are described in the Noyes Data Publication "Sausage Casing Technology" by Karmas (1974) at pages 259-347.
Cellulosic casing for the shirring operation is supplied in reels. The flat casing feed stock, drawn from a reel, is fed into a shirring machine where it is inflated with low pressure gas, usually air. The inflated casing is passed onto and along a mandrel and through an array of shirring rolls. In one form of shirring, the shirring rolls gather the casing about the mandrel into generally conical pleats nested one tightly against another. The inner folds of the pleats are formed against the mandrel and define the surface of an axial bore through the stick.
When a preselected shirred length has been attained, it is separated from the unshirred feed stock and moved longitudinally away from the array of shirring rolls for further processing. Such further processing may include, for example, a compaction operation where the shirred length is reduced and an operation where a closure is formed and inserted to stop or plug the bore at one end of the casing thereby forming a "closed" end. The other end of the casing is left open to permit mounting of the shirred stick onto a stuffing horn.
Separation of the last shirred end of the stick from the reel feed stock has been accomplished both manually and by automatic means. Separation generally leaves a loose length or "tail" of casing extending from the pleats at the last shirred end. This tail is not desirable particularly in shirred sticks for frankfurter production, as it detracts from both the appearance and use of the stick. For example, a tail at the open end may partly occlude the bore opening and thus interfere with the automatic loading of the shirred stick onto the stuffing horn.
Separation by other than a transverse cut through the casing often produces ragged ends having one or more loose tags of casing on one or both of the severed ends. A tag may separate from the casing and mix with the food product being stuffed into the casing. This is especially the case where the casing is stuffed with frankfurter emulsion and the tags are on the closed end of the stick which comes into direct contact with the food emulsion.
One common method for dealing with the loose tail is to remove it by manually peeling it from the shirred stick so that only tightly nested pleats remain at the end of the stick. Methods also have been employed to mold or dress the open end of frankfurter casing so that the tail is pressed tightly to the nested pleats.
Various methods have been proposed to reduce the length of the tail and the raggedness of the severed ends. For example, U.S. Pat. No. 4,547,932 discloses a guillotine severing method in which a blade cuts completely through the casing to provide a neat square-ended cut. While this method avoids a ragged end, it still leaves a tail at the open end of the stick. It also requires mandrel components that axially separate to provide a gap which permits a cutter to pass completely through the casing. Once the mandrel components are separated, it may be difficult to realign and reconnect them to shirr another stick.
Other methods have been proposed to sever the casing cleanly without the need to axially separate the mandrel. For example, in U.S. Pat. No. 3,878,978 a stream of liquefied carbon dioxide is directed against the casing until it becomes brittle from the cold. A force against the brittle casing shatters it without leaving a loose tail. However, small particles of frozen casing may be displaced into the bore of the stick and become entrained in the food product during stuffing.
U.S. Pat. Nos. 3,936,909 and 4,627,718 also describe improved methods of separating the shirred stick from the reel feed stock. The '718 patent describes a high pressure water jet which rotates around the casing to sever the stick from the reel feed stock. However, the use of water as the cutting medium may alter the moisture balance along the stick length. In the '909 patent an unshirred portion of casing is contacted about its circumference with a hot wire or is partially perforated by a cutter. The feed stock casing is then held while the shirred stick is moved away. This overstresses the weakened or partially perforated area and results in a separation of the unshirred casing from the shirred stick. This method requires that the casing be weakened at some point intermediate the shirred stick and unshirred length so that separating in this fashion inherently leaves a tail of casing extending from the last shirred and tightly nested pleats.